(1) Field of the Invention
The present invention relates to corrosion-resistant members and a producing process thereof.
(2) Related Art Statement
It is currently known that dense silicon carbide films are effective as liners in gas turbine parts and diesel engine parts, etc., and as antioxidant surface films for ceramic parts to be used in a high temperature atmosphere, etc. It is also known that surfaces of ceramic parts are covered with thin films of dense silicon carbide in some cases of semiconductor-producing apparatuses, etc. In order to form such thin films, the chemical gas phase growth method, the electrochemical gas phase growth method, the sputtering method, the spraying method, etc. are known. For example, since the gas phase method can form a high purity, dense and thin film having good properties, this method is frequently used.
Recently, it is demanded that not only super pure water and sterilized water but also hydrofluoric acid, nitric acid, hydrochloric acid, super high purity solutions containing mixed acids containing aqua regia or the like be treated, completely free from contamination with metallic ions or an organic material. There are demands for gas-tight parts to be exposed to reactive plasma gases such as CF4, NF3, ClF3, HF, HCl, Hbr or the like. Such reactive plasmas are all highly corrosive. Members which can maintain gas-tightness and contamination resistance for an extended time period under the environment in which the members are exposed to the above solution or gas having highly corrosive property having been demanded.
Although the inventors had made investigations to solve the above problem, they encountered difficulties. That is, in order that gastight parts may be used, for instance, for semiconductor-producing apparatuses for a long time period, a film of silicon carbide is required to be made thicker. On the other hand, a large volume of a vessel is required to treat a large amount of the solution or gas. In order to enable the vessel having such a large volume to treat a large amount of the solution or gas, it is necessary to cover a large-area surface of a sintered body with a gas-tight film of silicon carbide.
However, although such gas-tight parts are actually subjected to heat impact between room temperature and high temperatures, the heat impact causes the film of silicon carbide to be cracked and reduce the gas tightness thereof, if the silicon carbide film is enlarged in area and thickened. Consequently, impurities contained in the substrate dissolved into the solution or gas, which unfavorably causes pollution.
It is an object of the present invention to provide a corrosion-resistant member comprising a substrate made of a ceramic material and a thick film of silicon carbide formed on a surface of the substrate by chemical vapor deposition, covering this surface, whereby the corrosion-resistant member has high corrosion resistance, and is free from cracking of the film of silicon carbide even upon application of heat impact.
It is another object of the present invention to produce such a corrosion-resistant member.
The corrosion-resistant member according to the present invention is characterized by comprising a substrate made of a ceramic material and having a diameter of at least 200 mm, and a film of chemically vapor deposited silicon carbide having a thickness of not less than 0.5 mm and covering at least such a portion of the surface of the substrate that is to contact a corrosive material.
The process for producing the above corrosion-resistant member according to the present invention is characterized in that the step of forming the film of silicon carbide at a film-forming temperature by the chemical vapor deposition is followed by a step of thermally heating the film of the silicon carbide at a temperature higher than the film-forming temperature by not less than 50xc2x0 C. centigrade.
The film forming temperature is preferably not less than 1,400xc2x0 C. centigrade and not more than 1,500xc2x0 C. centigrade.
These and other objects, features and advantages of the invention will be well appreciated upon reading the following description of the invention when taken in connection with the attached drawings, with the understanding that some modifications, variations and changes may be easily made by the skilled person in the art within the purview of the invention.